Pivot for indicating instruments



Patented May 25, 1937 PATENT OFFICE 2,081,820 PIVOT FOR INDICATING INSTRUMENTS Floyd 0. Kelley, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York No Drawing.

6 Claims.

The present invention relates to pivots for indicating devices and more particularly to pivots which are suitable for use in aircraft compass indicators.

Prior to the present invention, pivots generally employed in air compass indicators have been characterized by a lack of sensitivity due to friction between the pivot and jewel bearing. These pivots are relatively small and have a bearing point with a radius of only about 3 mils. It has been difficult to produce a pivot of this character which is hard enough to withstand shock and wear and yet not so brittle that the point will break oif.

It is one of the objects of the present invention to provide an instrument pivot which has a low coefficient of friction, which is non-corrosive,

non-magnetic and which is hard and tough and has a relatively long life. Other objects will appearherein'after.

The pivot material employed is made by drawing substantially pure tantalum or a tantalum such as nickel and then inserted in a furnace heated to a temperature, preferably in the neighborhood of 500 C. Nitrogen which has been purified to a high degree is then supplied tothe furnace so that the pivots are substantially surrounded by a molecular nitrogen atmosphere. The pivots are maintained in the furnace for a period of time varying from about 20 to 30 minutes. The time employed in the nitriding process however may be shorter or longer than that indicated depending upon whether the nitriding temperature is higher or lower than 500 C. The

Application September 30, 1933, SeriaLNo. 691,737

product thus obtained has such a low coeflicient of friction that the wear on the pivot is very slight. It is also non-corrosive and non-magnetic, hard and tough.

Although the pivot to be nitrided may consist substantially entirely of tantalum I prefer to employ a tantalum alloy containing an appreciable amount up to about l /2% tungsten. The addition of the tungsten to the tantalum provides a product of increased hardness and toughness which may be hardened in the same manner as the tantalum pivot. It is also more easily shaped and polished.

Although I have described the present invention particularly in connection with aircraft compass indicators, it is obvious that its use is not limited to such indicators but that it may be employed as a pivot or jewel bearing in any type of indicating instruments. It is also obvious that my invention may be employed wherever a metal having the qualities herein specified is required.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A pivot for indicating devices consisting mainly of tantalum and having a nitrided surface thereon.

2. A-pivot for aircraft compass indicators, said pivot consisting mainly of tantalum and having a. nitrided surface thereon.

3. A pivot for indicating instruments compris- .ing an alloy containing an appreciable quantity and up to '7 /2% tungsten with the remainder tantalum, said alloy having a nitrided surface thereon. v

4. A pivot for aircraft indicating. compasses, said pivot comprising an alloy containing an appreciable quantity up to about 7 7., tungsten with the remainder tantalum, said alloy having a nitrided surface thereon.

5. In an indicating device, a pivot member and a cooperating bearing member therefor, said members each consisting mainly of tantalum and having a nitrided surface thereon.

6. A hearing consisting mainly of tantalum and having a nitrided surface thereon.

. FLOYD C. KELLEY, 

